CODEWITHSUNDEEP
c
JhonSmithOptional
JhonSmithOptional

Reputation: 31

why function doesnt called?

I am writing the following program in C.

This program is a adjacency matrix, which asks the user to set a connection between nodes and than check to see if there is a connection between node A and node B.

# include <stdio.h>
# include <stdlib.h>

#define N 11
#define FALSE 0
#define TRUE 1

typedef int adj_mat[N][N]; /*defining adj_mat */

int path (adj_mat A, int u, int v);

The main function asks user to make directed graph and then asks for the user to enter two nodes to check if they exists a connection between node A and node B.

int main()
{
    adj_mat Matrix; /*intializing a new graph adjacency matrix. 
                     on this moment nodes are disconnected every cell contains zero */
    int dadnode, sonnode; /*intializing dad node and son node*/

    printf("Hello. Enter now the pairs of connected nodes.\n");    
    printf("enter EOF after finishing of connecting all the nodes\n");

    do {  /*here user enter the nodes to connect */
        printf("Enter the number of first node\n"); 
        scanf("%d", &dadnode);
        printf("Enter the number of second node\n");
        scanf("%d", &sonnode);

        if ((dadnode < sonnode) && (sonnode <= N) && (dadnode > 0)) /*checking if nodes are legal*/
            Matrix[dadnode][sonnode] = 1; /*if legal - connect*/
    } while ( (dadnode != EOF ) && (sonnode != EOF)); /*until user enter EOF */

    printf("Now enter u and v nodes to check if exists way from u node to we node\n");
    /*here user enter the nodes to check */
    printf("Enter the number of u node\n"); 
    scanf("%d", &dadnode);
    printf("Enter the number of v node\n");
    scanf("%d", &sonnode);

    if ((dadnode < sonnode) && (sonnode <= N) && (dadnode > 0)) /*checking if nodes are legal*/ {
        if( path(Matrix,dadnode,sonnode) == TRUE ) /*if exisits way from u to v*/
            printf ("Exists way from node u to node v ");  
    }
    else printf ("Not exists way from node u to node v ");         
}

The following function returns TRUE if exists way from u(dad node) to v(son node) otherwise returned FALSE

int path (adj_mat A, int u, int v) {
    if (v >= u) /*no sense to check if dad node yonger than son node or dad of himself */
        return FALSE; 
    int nodenum; /*number of node*/
    /* "nodenum = v - 1" because node v cannot be son of node >= v */
    for(nodenum = v - 1; nodenum > 0; nodenum-- ) {
        if (A[nodenum][v] == TRUE) /*dad detected*/
        {
            if (nodenum == u) {
                return TRUE; //complete
            } else if (path (A, u, nodenum)) {
                return TRUE; //maybe dad is a node that we are looking for (recursion)
            }
        }
    }  
    return FALSE; /*all parents of v node were cheked and noone of them isnt u node*/
}

Finally, I run this in gdb (ubuntu). 

do {  /*here user enter the nodes to connect */
    printf("Enter the number of first node\n"); 
    scanf("%d", &dadnode);
    printf("Enter the number of second node\n");
    scanf("%d", &sonnode);

    if ((dadnode < sonnode) && (sonnode <= N) && (dadnode > 0)) {/*checking if nodes are legal*/
        Matrix[dadnode][sonnode] = 1; /*if legal - connect*/
    }
} while ( (dadnode != EOF ) && (sonnode != EOF)); /*until user enter EOF */

Why when I trying to stop this loop (from main function) by pressing Ctrl+d, the loop will continue and stop only after a pair of numbers are found where one of the numbers is -1 ?

Ok, enter "-1" and then the main function should calls the path() function to check if node a and node b are connected. If they are, then it should output a message according the result of path(Matrix,dadnode,sonnode).

However, instead of this behaviour I get the message "Program exited normally." Why do I get this message?

Does main function even call the path() function? I'm not sure what the error in my code is...

Upvotes: 0

Views: 296

Answers (1)

Apples
Apples

Reputation: 3225

EOF is defined as (-1) in stdio.h, however when you use Ctrl + D to send an EOF message, you're sending a different character value (4). The EOF define of (-1) is meant to be the return value of functions that fail due to an end-of-file or other error. So instead of comparing your input value (dadnode or sonnode) to EOF, you should compare the return value of scanf() to EOF.

The return value of scanf() is the number of items read (in your case, it should only be 1), or EOF if the user sends Ctrl + D (Windows users will have to send Ctrl + Z).

Example:

int dadnode, sonnode;
int result;

while (true)
{
    result = scanf("%d", &dadnode);
    if (result < 1) break;

    result = scanf("%d", &sonnode);
    if (result < 1) break;
}

Upvotes: 2

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